Generally, permanent magnet rotors have permanent magnets for a field and a yoke for forming magnetic paths, and are formed by inserting the permanent magnets for the field into slots formed in the yoke.
FIG. 25 shows a conventional permanent magnet rotor in an exploded state. A conventional permanent magnet rotor 221 has a yoke 222 and permanent magnets 223 for a field. The yoke 222 is formed by laminating a large number of silicon steel sheets 224. The yoke 222 has magnetic poles 225 formed on the outer periphery. At the bases of the magnetic poles 225, slots 226 are respectively formed at the same distance from a rotatable shaft 230 to insert the permanent magnets 223 for the field. Besides, each silicon steel sheet 224 is pressed to form caulking sections 227 recessed at equal intervals. The silicon steel sheets 224 are integrally laminated by mutually press-fitting the caulking sections 227.
The permanent magnets 223 for the field are formed to a size capable of being housed in the slots 226. In assembling the permanent magnets 223 for the field, the yoke 222 is shrinkage-fitted to the rotatable shaft 230, when a temperature of the yoke 222 is lowered, an adhesive is applied to the surfaces of the permanent magnets 223 for the field, which are then inserted in the slots 226 with their same magnetic poles opposed to each other as shown in the drawing. Arrow Q in the drawing indicates the direction that the permanent magnets 223 for the field are inserted.
On the other hand, for the permanent magnet rotor 221 which cannot use an adhesive because of its application conditions, the permanent magnets 223 for the field are formed so as to be fitted in the slots 126 without leaving any gap. When a temperature of the yoke 222 is lowered, the permanent magnets 223 for the field are pushed in the direction Q shown in the drawing by a pneumatic device so as to be forced into the slots 226. In addition, a non-magnetic balance weight 231 having the same diameter as the maximum diameter of the yoke 222 is press-fitted and fixed to the rotatable shaft at one end of the yoke 222.
But, in the above conventional permanent magnet rotor which uses the adhesive to be applied to the outer periphery of the permanent magnets for the field and inserts them into the slots of the yoke, the magnetized permanent magnets for the field are difficult to be inserted into the slots because they are attracted by the magnetic rotatable shaft, and the magnetized permanent magnets for the field are inserted with N and S poles in wrong directions.
And, there is a problem that when the permanent magnet rotor is operated in a refrigerant or pressurizing fluid, the adhesive is dissolved with the refrigerant or pressurizing fluid and the permanent magnets for the field come out.
And, to fix the balance weight to the end of the yoke, it is generally fixed to the rotatable shaft, but a delicate press-fitting size is required between the balance weight and the rotatable shaft because the balance weight has the shape of a fan. When the balance weight is fixed to the rotatable shaft, since the balance weight has a shape to cover the maximum outer diameter of the yoke, the passage of the refrigerant between magnetic poles is interrupted, and it is necessary to dispose the refrigerant passage at another position, e.g., the outer diameter of the stator. Besides, the balance weight can be fixed only after fixing the yoke to the rotatable shaft.
On the other hand, in the conventional permanent magnet rotor which directly forces the permanent magnets for the field into the slots of the yoke without using an adhesive, a large force is used to press-fit the permanent magnets for the field, and this force sometimes breaks the permanent magnets for the field.
And, the above permanent magnet rotor is required to have a high processing precision for fitting the permanent magnets for the field in the slots of the yoke in view of a dimensional consistency, making it difficult to produce the permanent magnet rotor.
Furthermore, to press-fit the surface-treated (plated) permanent magnets for the field into the yoke, plating is removed. As a result, there are disadvantages that fixing strength is lowered, and rust occurs.
In view of the above, a first object of this invention is to provide a permanent magnet rotor which prevents the permanent magnets for the field from falling out due to a refrigerant or pressurizing fluid and can be produced easily.
As to a compressor, technology is generally known that a drive motor and a compression device are disposed in series within a sealed vessel in which a refrigerant and an oil flow, and permanent magnets for a field are inserted into a rotor of the drive motor.
FIG. 26 is a longitudinal sectional view showing a conventional refrigerating cycle compressor. This refrigerating cycle compressor which is wholly designated by reference numeral 500 is provided with a sealed vessel 510 in which a refrigerant flows. The vessel 510 includes a compression device (not shown) and a drive motor 520 which are vertically disposed in series.
The drive motor 520 comprises a rotor 700, a stator 600 and a drive shaft 710. The stator 600 comprises a stator core 610 and an exciting coil 620. The rotor 700 includes a rotor yoke 720, permanent magnets 730 for a field, a spacer 740 and a balancer 750. The rotor yoke 720 is formed by laminating a large number of silicon steel sheets 760. The rotor yoke 720 has magnetic poles 770 on its outer periphery, and the magnetic poles 770 have at their bases slots 780 for inserting the permanent magnets 730 for the field.
The permanent magnets 730 for the field are formed into a size so as to be inserted into the slots 780, and their surfaces are not treated.
To assemble a refrigerating cycle compressor, the rotor yoke 720 is shrinkage fitted to the drive shaft 710 which is previously disposed within the sealed vessel 510. Specifically, the rotor yoke 720 is heated to about 450.degree. C. to expand a rotatable shaft hole at the center so as to have a slightly large diameter and fitted to the rotatable shaft 710 while it is still hot. When the rotor yoke 720 is cooled, the expanded rotatable shaft hole contracts, and its through hole tightly holds the rotatable shaft 710. When the compressor is used, a temperature of the compressor rises to about 130.degree. C., but since the rotatable shaft 710 is also expanded, the holding of the rotatable shaft 710 by the rotor yoke 720 is not lowered.
And, the permanent magnets 730 for the field are inserted into the rotor yoke 720. Specifically, after cooling the rotor yoke 710, the permanent magnets 730 for the field which are not magnetized nor surface-treated and wrapped in rust preventive paper are inserted into the slots 780. And, after inserting the permanent magnets 730 for the field, the non-magnetic spacer 740 is press-fitted to the end of the rotor yoke 720 to fix the permanent magnets for the field in the axial direction, and the magnetic balance weight 750 for keeping a dynamic balance of the compression device is press-fitted to about the end of the spacer 740. In the drawing, arrow Q indicates the direction that the permanent magnets 730 for the field are inserted.
After fitting the above components, a lid (not shown) of the sealed vessel 510 is closed, a high current is applied to the exciting coil 620, the rotatable shaft 710 is locked, the permanent magnets 730 for the field are magnetized, and hot air is blown to dry the interior of the sealed vessel 510 to evaporate moisture.
Since the above prior art inserts the permanent magnets for the field whose surfaces are not treated into the slots of the rotor yoke, it is rather difficult to prevent the occurrence of rust until the permanent magnets for the field are fitted, and even after inserting into the slots, since a refrigerant and an oil are pressurized to flow within a pressure container where a motor operates, there is a disadvantage that they may penetrate into the interior of the material for the permanent magnets for the field to fuse the magnets.
In view of the above, it is recently known to treat the surfaces of the permanent magnets for the field which are used for the compressor. In this case, each magnet has its two opposite faces pinched by needle-shaped fixing electrodes, a current is passed to the electrodes, and the magnet is dipped to be nickel plated in a plating bath, but the parts of the magnet material which are in contact with the fixing electrodes are not plated, exposing the magnet material.
When the permanent magnets for the field which have been electrically nickel plated are inserted into the slots of the rotor yoke, it is necessary to apply a repairing material to the electrode marks to prevent rust from occurring on the electrode marks (the plating with the repairing material applied to the electrode marks will be hereinafter referred to as nickel plating with electrode marks), but even when repaired, there is a problem that the repairing material is dissolved into the refrigerant or oil. Furthermore, with a high temperature for the shrinkage fitting and the hot air drying, the repairing material is peeled easily due to a difference in expansion coefficient between the repairing material and the plating, and because of a heat resisting strength lowered due to a difference in material, the dimensional management of the magnets including the repaired parts is difficult.
In addition, since the nickel plating with electrode marks using the fixed electrodes concentrates a plating current to the ends of the permanent magnets for the field, the ends generally tend to have thicker plating than the center (20 .mu.m to 50 .mu.m), making it difficult to manage the thickness size, and when the plated film becomes thick, a residual stress in the film increases to cause a disadvantage of deteriorating the adhesion.
On the other hand, without using the above electroplated permanent magnets for the field, there is a case of inserting electroless plated permanent magnets for a field into a rotor yoke. In this case, the electroless plated permanent magnets for the field are separately heated, the rotor yoke is shrinkage fitted to the rotatable shaft, then the heated permanent magnets for the field are inserted into the slots of the rotor yoke. To use the electroless plated permanent magnets for the field, there are disadvantages that a process takes a long time and it is difficult to fix the magnets because three steps are adopted for the thermal treatment of the electroless plated permanent magnets for the field, the shrinkage fitting of the rotor yoke to the rotatable shaft, and the insertion of the permanent magnets for the field into the slots of the rotor yoke.
A second object of the invention is to provide a permanent magnet rotor and its production method in which electroplated permanent magnets for a field and electroless plated permanent magnets for a field improve a permanent magnet rotor inserted into the slots of a rotor yoke and its production method; when the electroplated permanent magnets for the field are used, the plating is substantially uniform at the center and ends of the permanent magnets for the field and does not have an electrode mark; and the process can be simplified and the production time can be shortened, which are also applied to the electroless plated permanent magnets for the field.